Unfortunately the situation on Android is that other apps cannot do anything with WhatsApp, and there's fuck all you can do about it as a user.
I shouldn't need Google special-casing Gemini to allow LLMs to interact with my messages. I should be able to wire up Tasker to WhatsApp on one end, and to OpenAI or Anthropic models of my choice via API calls on the other end. Alas, Android is basically like iPhone now, just with more faux choice of vendors and less quality control.
WhatsApp has been forced by the EU to provide access to third parties. If there's any app that third party apps can interact with, it's WhatsApp.
I also can't really find the mechanism at use here. I don't know if WhatsApp is exposing some kind of dedicated assistant API that an alternative assistant (the one you can pick in the settings) might be able to use.
I'll need to check again. Maybe it's my rusty Android skills, but last time I checked (circa a year ago), I got the impression it's going out of its way to stay fully opaque from the outside.
It's also notoriously the one popular app that intentionally doesn't offer any kind of API access for normal users - it only has one to allow companies to automate advertising bots.
Users always have a way to compromise their own security, and short of taking away their freedom completely (e.g. putting them in a mental hospital) that's not possible to fix.
Sacrificing human freedom in the name of security is a long, dark, and well-trodden path that I don't think we ought to venture down any further.
I shouldn't need Google special-casing Gemini to allow LLMs to interact with my messages. I should be able to wire up Tasker to WhatsApp on one end, and to OpenAI or Anthropic models of my choice via API calls on the other end. Alas, Android is basically like iPhone now, just with more faux choice of vendors and less quality control.